1. Field of the Invention
The present invention relates to a method and an apparatus for assuring quality control wherein a degree of quality of raw material is properly controlled, e.g., when cement is produced in accordance with a so-called mining site control process, while rocks of limestone excavated from a plurality of pit faces on a mine are collected at a specific collecting location at the foot of a mountain.
2. Description of the Related Art
To facilitate understanding of a conventional quality control, the aforementioned mining site quality control process employed when cement is produced will be described below with reference to its current state.
As is well known, arrangement of CaCO.sub.3 constituting a main component of limestone usable as raw material when cement is produced becomes a significant problem for the purpose of maintaining good quality control.
Usually, rocks of limestone are excavated from a plurality of pit faces on a mine in such a manner that limestone rocks having a content of CaCO.sub.3 more than 92% are excavated from several pit faces and other limestone rocks having a content of CaCO.sub.3 of about 5% are excavated from the remaining pit faces. These excavated rocks are conveyed by a plurality of dumptrucks to a specific collecting location (in the form of a shaft) at the foot of a mountain, whereby arrangement of CaCO.sub.3 is made in an optimum manner by mixing them at the collecting location. To assure that a certain degree of quality predetermined as a target with respect to rocks mixed at the collecting location (in the shaft) is maintained for the production of cement (usually, 92% represents a preferable degree of quality for production of cement), i.e., rocks to be mixed with each other are collected at a specific rate for maintaining the target degree of quality, the following steps have been hitherto performed to improve accuracy in relation to the mining site control process.
These steps will be noted below.
(1) Before conveying operations are performed by dumptrucks (usually, at a day before the conveying operations), limestone rocks (comprising rocks having a higher content of CaCO.sub.3 and rocks having a lower content of the same) are excavated from the respective pit faces using drilling machines and their powders obtained by drilling operations are chemically analyzed to determine their degree of quality. This is intended to clarify a relationship between each pit face (excavating location) and grade of quality of limestone excavated therefrom. PA1 (2) Then, (usually, at the same day as the conveying operations) a plan for operating respective dumptrucks is settled with reference to the thus determined degree of quality of rocks excavated from each pit face (in many cases, plural kinds of dumptrucks of which loading capacity is different from each other are operated). PA1 (3) While a time of movement of the dumptrucks to loading locations (pit faces) and a shaft (dumping pit) and the number of dumping operations are properly controlled in accordance with the settled operation plan, rocks excavated from the respective pit faces are collected in the shaft. Such controlling is effected via wireless communication between one vehicle in which a person in charge of calculation rides and other vehicles. For example, a notice "No. 1 dumptruck and No. 3 dumptruck should move toward No. 1 pit face and No. 2 pit face where rocks having a higher content of CaCO.sub.3 are excavated. In the meantime, No. 2 dumptruck should convey rocks having a lower content of the same in No. 3 pit so that they are dumped in the shaft." is issued from the person. PA1 (4) Each vehicle is equipped with two manually operable counters in its cabin allocated to the respective loading locations (one of them being provided for rocks having a higher content of CaCO.sub.3 and the other one being provided for rocks having a lower content of CaCO.sub.3). Each time loaded rocks are dumped in the shaft, an operator in each vehicle manually actuates one of the counters which corresponds to the content of rocks. Values derived from the counters in that way are later summed so that they are used for the purpose of periodic quality control for rocks dumped in the shaft and confirmation of operations performed by the dumptrucks, e.g., per day in unit. PA1 (5) Rocks dumped in the shaft (collecting location) are extracted from the middle part of the latter so that they are crushed by a crusher. Crushed rocks are then sieved under the influence of vibration and fine rocks each having an adequate grain size are conveyed to a cement factory via a belt conveyor. It should be noted that a predetermined quantity of fine rocks are subjected to sampling at a constant time interval (usually, every seven minutes and thirty seconds). Further, the rocks which have been collected by sampling are chemically analyzed at a constant time interval (usually, every two hours and thirty minutes to three hours) to confirm the result derived from adjustment of the content of CaCO.sub.3.
With such quality control, it is possible to maintain a degree of quality of collected rocks to some extent with certainty, particularly in response to the accuracy set by the above operation plan. In practice, however, it is very complicated to prepare an operation plan itself, because the latter requires a number of elaborate calculations. Thus, it is difficult to prepare such an operation plan with high accuracy.
With respect to a quantity of conveyance for rocks to be handled in accordance with the operation plan, a fixed value set with a standard loading capacity for each vehicle used as a reference is employed (e.g., in case of a dumptruck having a loading capacity of 35 tons, its quantity of conveyance is always set to 35 tons and in case of a dumptruck having a loading capacity of 70 tons, its quantity of conveyance is likewise always set to 70 tons). Accordingly, as a conveying operation progresses, there arises a problem that a value representative of the degree of quality of collected rocks involves error which gradually increases.
Thus, quality control can not be carried out to the extent expected, in spite of the fact that the operation plan has been prepared with much difficulty. Further, it is practically difficult to adjust execution of the quality control.
Additionally, with the conventional controlling method, wireless communication between vehicles is required. Another troublesome problem is that confirmation of completion of the noticed conveying operation (i.e., actuation of the aforementioned counters) is entrusted to operators for the respective vehicles. If actuation of the counters is forgotten or neglected, periodic data derived from execution of quality control becomes meaningless.
These problems arise not only in case of production of cement but things are almost same with a method of adjusting arrangement of collected raw material and executing quality control for the latter in accordance with the mining site control process.